1. Field of the Invention
The present invention relates to a zoom lens barrel and an image pickup apparatus provided with the lens barrel.
2. Description of the Related Art
An image pickup apparatus such as a digital camera mounted with a zoom lens barrel has been demanded to have a high photographing magnification and a thin thickness. This poses a problem that a movement stroke of a photographing lens group must be increased, while reducing the lens barrel size.
Nevertheless, there has widely been used a camera having a lens barrel provided with an iris diaphragm for changing the amount of incident light to cope with various photographing conditions. In such a camera, a movement of a photographing lens group is restricted by the iris diaphragm provided in the lens barrel. In a case, for example, that the iris diaphragm is disposed between photographing lens groups, these lens groups cannot relatively be moved toward each other much closer than the thickness of the iris diaphragm.
Thus, there has been proposed an image pickup apparatus having a lens barrel in which a diaphragm is provided on a portion of an object-side lens surface of a lens (lens group) (see, Japanese Laid-open Patent Publication No. 2004-053633).
However, the diaphragm of the proposed image pickup apparatus has an aperture of a fixed diameter, and accordingly, if a target F number in design is determined at one of wide-angle and telephoto ends, an F number at another of the wide-angle and telephoto ends is determined by a focal distance. Thus, if an attempt is made to increase the diaphragm aperture diameter at the wide-angle end, the diaphragm aperture diameter at the telephoto end increases. To obviate this, the number of lenses must be increased, so that the lens barrel size cannot be reduced.
There has also been proposed a lens barrel frame that includes a lens having a convex spherical surface portion (Japanese Laid-open Patent Publication No. H10-111444).
However, in the lens barrel frame disclosed in Japanese Laid-open Patent Publication No. H10-111444, the diaphragm aperture diameter is merely switched between two cases where the convex spherical surface portion of the lens intrudes into the diaphragm blade aperture and where it does not intrude into the aperture. It is therefore impossible to change the diaphragm aperture diameter steplessly or in multiple steps according to zoom control.